Carboxylic acids (e.g., acetic acid) or derivatives thereof (e.g., methyl methacrylate) have been produced industrially by use of carbonylation reactions. For example, Japanese Patent Application Laid-Open No. 54011/1973 (JP-48-54011A) discloses a carbonylation method in which an olefin, an alcohol or an ester thereof, a halide, or an ether derivative is allowed to react in a liquid phase with carbon monoxide in the presence of a catalytic system containing a rhodium or iridium component and an iodine or bromine component. In this process, at least a part of a liquid reaction product is supplied, without heating, to a separation zone which is substantially low in pressure to vaporize or evaporate at least a part of the above-mentioned carbonylation product, the vaporized carbonylation product is taken out, and the residual liquid reaction product is recirculated to the above-mentioned reaction zone. This document describes the removal of unreacted carbon monoxide from the reactor. Japanese Patent Application Laid-Open No. 321847/1994 (JP-6-321847A) discloses a carbonylation product recovering method for maintaining the concentration of water in the liquid component at least at 0.5 weight % in which an iridium catalyst is used as a carbonylation catalyst, wherein a vapor component containing the carbonylation product and a liquid component containing the iridium catalyst are produced by vaporization of the reaction product and the vapor component is separated from the liquid component. This document illustrates the discharge of unreacted carbon monoxide as exhaust gas from the reactor.
Japanese Patent Application Laid-Open No. 508594/1998 (JP-10-508594A) proposes a method comprising the steps of producing a carboxylic acid in a first region by liquid phase carbonylation in the presence of a rhodium catalyst, partially vaporizing the reaction mixture in a second region, purifying a vapor fraction containing the produced carboxylic acid and recycling the non-vaporized liquid fraction containing the catalyst to the first region, wherein carbon monoxide is supplied to the non-vaporized liquid fraction produced from the second region by avoiding the return of carbon monoxide to the second region in order to prevent the loss of carbon monoxide.
Japanese Patent Application Laid-Open No. 95723/2000 (JP-2000-95723A) discloses a control method for a process of producing acetic acid by carbonylation, wherein the flow of carbon monoxide passing through a control valve is measured, the average value of the carbon monoxide flow per a predetermined time is calculated, a fixed value is added to this average carbon monoxide flow to calculate the maximum flow rate of carbon monoxide, and the operation is performed so that the flow rate of carbon monoxide into the reactor does not exceed the maximum flow rate.
However, these carbonylation methods are pressurized reaction systems in which the reaction is carried out by pressurizing carbon monoxide with a compressor. In order to inhibit the occurrence of surging in such pressurized reaction systems, carbon monoxide is supplied to the reaction system with maintaining a constant pressure and a constant flow rate at the inlet and the outlet of the compressor. Meanwhile, the pressurized reaction system, in which the reaction is carried out under a predetermined applied pressure, causes fluctuation or variation of the consumption rate of carbon monoxide with varying reaction temperatures. In particular, in an actual producing or manufacturing plant the consumption rate of carbon monoxide is significantly fluctuated even when the reaction temperature in the reaction system slightly varies. Accordingly, in order to prevent a pressure drop in the reaction system, carbon monoxide in an excess amount over the consumption rate of carbon monoxide at a steady state (reference consumption rate) is supplied to the reaction system, as a reference flow rate, from the outlet of the compressor on the assumption that the consumption rate is large. Therefore, in the case where the consumption rate of carbon monoxide is less than the reference consumption rate in the reaction system, an excess of carbon monoxide in the reaction system is emitted or discharged and burned at the outside of the reaction system as a flare for retaining the pressure of the reaction system at a given value, and ensuring a stable operation. However, in such a system it is impossible to utilize carbon monoxide effectively, resulting in a great economical loss.
Further, in a carbon monoxide-producing plant (carbon monoxide-manufacturing plant), and a producing plant (e.g., acetic acid-producing plant) in which the carbonylation reaction is conducted with carbon monoxide produced by the carbon monoxide-producing plant, each of the carbon monoxide feed system and the carbonylation reaction system (or reaction system including separation and purification) is independently controlled. It is therefore impossible to reflect fluctuation factors in the reaction system (such as a pressure fluctuation) when controlling the carbon monoxide-producing plant and the feed system. Thus, it is difficult to more efficiently reduce the emission or discharge of carbon monoxide and to effectively utilize carbon monoxide for the carbonylation reaction.
It is, therefore, an object of the present invention to provide a control method and a control apparatus in which the gaseous reactant (such as carbon monoxide) is effectively used for the reaction in the pressurized reaction system.
Another object of the present invention is to provide a control method and a control apparatus in which the emission (or discharge) of the gaseous reactant is inhibited or suppressed and which is useful for subjecting the gaseous reactant to a reaction with economical advantages.
It is still another object of the present invention to provide, in a pressurized reaction system (such as a carbonylation reaction system) in which an excess amount of the gaseous reactant over the reference flow rate is continuously supplied industrially, a control method and a control apparatus for utilizing the gaseous reactant effectively for a reaction even when the consumption rate of carbon monoxide varies in the reaction system.